The overall goal of this Core Facility is to perform preclinical toxicological studies on two potent delta opioid receptor antagonists c[D-Pen2,D-Pen5]enkephalin (DPDPE) and biphalin, to prepare sterile pyrogen free injectable DPDPE and biphalin solution for preclinical toxicological studies at The University of Arizona and by Dr. Yaksh at the University of San Diego. Specifically, we will perform intravenous acute toxicology studies for DPDPE and biphalin in rats and dogs giving daily i.v. injections of either agent or 30 and 5 days, respectively. At the end of dosing the animals will be euthanized and organs will be collected, weighed and tissue slices prepared for blinded histopathological studies. If not toxic, the data from these studies will be combined with the I.T. toxicological studies of Dr. Yaksh and incorporated into an investigator-sponsored investigational New Drug Application (INDA) for each agent.